1. Field of the Invention
The present invention relates to a method for automatic optimization of finite difference grids for use in a simulator to perform simulation for computational fluid dynamic analysis (hereinafter referred to as "CFD simulator") or the like, whereby the spacings of analytic grids, generated by a finite difference method in the Cartesian coordinate system, are automatically adjusted, before the execution of simulation, according to the shape to be analyzed of the simulation model and, at the same time, the spacings are also automatically adjusted during the simulation according to the rates of variation of physical quantities, and a computer-readable medium in which a program for such automatic optimization is recorded.
2. Description of the Prior Art
When the spacings of analytic grids generated by a finite difference method (hereinafter referred to as "finite difference grids") in a CFD simulator or the like are to be optimized, optimization by a solution adaptive grid method, as described in the "AIAA Journal", Vol. 24, pp. 948-954, has been studied for use in the boundary fitted coordinate system that has coordinate axes along the boundary of an obstacle, but such a method involves a problem that its effective use requires the user to be experienced in parameter setting for optimization and to go through trials and errors, and another problem that it lacks versatility because it has been used for such a specific purpose as capturing shock waves.
There also are other methods including one of supplementation with a preset number of grids for use in the so-called Cartesian coordinate system, wherein coordinate axes orthogonally cross each other, such as the method disclosed in the Japanese Patent Application Laid-open No. Hei-6-221956 and another which requires the calculation of complex load coefficients for optimization, such as the one disclosed in the Japanese Patent Application Laid-open No. Hei-7-63643.
However, all these methods for use in the Cartesian coordinate system are to optimize grid spacings during simulation but not to optimize the spacings of initial grids. Therefore, where initial grids are to be set in the Cartesian coordinate system, the flow should be empirically predicted and, where the initial grids that are set would influence the result of simulation, simulation has to be repeated on a trial and error basis. Therefore, there is the problem that, depending on how the initial grids are set, the quantity of calculations or optimization rather increases instead of decreasing.
An object of the present invention, intended to obviate these problems of the prior art, is to provide a method for automatic optimization of finite difference grids, which can make it possible to obtain solutions at a higher level of accuracy than any conventional method can from an early stage of simulation, to dispense with the setting of specific parameters such as in a solution adaptive grid process, and to shorten the time required for calculation for optimization by optimizing the spacings of analytic grids in the generation of initial grids.
Another object of the invention is to provide a method for automatic optimization of finite difference grids, which makes it possible to eliminate regeneration of grids and repetition of simulation, and to reduce the loads of man-hours and cost by using automatically optimized initial grids.
Still another object of the invention is to provide a method for automatic optimization of finite difference grids, which makes it possible to provide solutions at an even higher level of accuracy of automatically adjusting the spacings of grids during simulation as well.
The present invention also has an object to provide a computer-readable medium in which is recorded an automatic optimization program for causing a computer to execute said automatic optimization of finite difference grids.